In general, embossed carrier tapes for mounting electronic components such as IC or LSI on electronic equipment are made from sheets that are constituted by a thermoplastic resin, such as a vinyl chloride resin, a styrenic resin or a polycarbonate resin, and thermoformed into an embossed shape. These embossed carrier tapes need measures for preventing electrostatic damage with respect to the above electronic components. For example, non-transparent sheets such as sheets constituted from a resin composition comprising a conductive filler such as carbon black in a thermoplastic resin to achieve a specific surface resistivity of at most 108 Ω/sq. have been used. On the other hand, it is advantageous for embossed carrier tapes for storing electronic components which are less likely to be destroyed by electrostatic damage, e.g., capacitors, to enable visual inspection of the stored electronic components from the outside or detection of the text described on the components. Therefore, transparent type embossed carrier tapes with a substrate made from the above thermoplastic resins with relatively good transparency have been used.
However, due to demands to miniaturize these electronic components or to increase the mounting speed, not only the problem of destruction of components caused by electrostatic damage, but also the problem of poor mounting caused by attachment or transfer of components to carrier tapes because of static has surfaced. Transparent type carrier tapes have also been required to have antistatic properties as antistatic measures.
As the sheets used in transparent type embossed carrier tapes, there are styrenic resin sheets, such as sheets comprising a mixture of a commonly used polystyrene resin and a styrene-butadiene block copolymer (Patent Document 1 etc.) and sheets constituted from a rubber modified styrene polymer comprising a styrenic monomeric unit and a (meth)acrylic acid ester monomeric unit (Patent Document 2 etc.). Carrier tapes are required to maintain a balance of physical properties such as transparency, impact resistance, folding strength and formability based on their state of use. To date, many studies have been made to improve these properties or to obtain a good balance of physical properties. Further, as the technique for providing antistatic properties, for example, coating the surface with an antistatic agent or blending an antistatic agent in the resin has been performed.
However, for a conventional transparent type antistatic sheet, when the antistatic properties were emphasized, the problem of low folding strength of the sheet and easy cracking or splitting of the sheet with respect to the direction of extrusion and the problem of reduced transparency occurred. In particular, while indicators such as haze and total light transmittance have been generally used for transparency, with advances in component miniaturization, even when the haze or total light transmittance value is good, when examining components across the carrier tape, visibility, i.e., distinction of the text etc. described on the components, is sometimes difficult.
Moreover, usually when producing a laminated sheet by co-extrusion forming, portions called “ears” are formed by trimming of the two ends of a die-extruded sheet. Portions that are not made into products, such as the “ears” or the beginning of the sheet during winding, are ground, re-made into pellets and, for example, added to the raw material of a core layer, to be reused as recycled materials in general. When considering the productivity of laminated sheets, even if such a recycled material is added, it is very important for the resulting sheet to have good properties and to enable examination across a carrier tape as described above. However, conventional laminated sheets had problems of markedly reduced transparency and visibility when recycled materials were added.